Mike Pence visited the Demilitarised Zone that separates the two Koreas on Monday, on the first leg of his first overseas tour since becoming vice president

US Vice President Mike Pence arrives in Tokyo on Tuesday bringing a renewed commitment to Japan's security amid a growing threat from a nuclear armed North Korea.

Throughout his bareknuckle election campaign, US President Donald Trump repeatedly called into question a mutual defense treaty between Japan and the United States, suggesting Tokyo should pay for its own security.

But now, Pence will try to reassure his jittery hosts that those decades-old security commitments are ironclad, a necessity made more acute as tensions rise over Pyongyang's latest missile test and Washington's refusal to rule out military action against the regime.

Defying international pressure, the North on Sunday test-fired another missile and fears are growing it may also be preparing a sixth nuclear test.

North Korea could react to a potential US strike by targeting South Korea or Japan, and officials in Tokyo and Seoul have been ill at ease with the more bellicose language deployed by Trump's administration.

During a visit to the Demilitarized Zone between North and South Korea on Monday, Pence pointed to the new president's recent strikes on a Syrian airbase and an Islamic State complex in Afghanistan as a warning to Pyongyang not to underestimate the administration's resolve.

"All options are on the table" in pushing for an end to Pyongyang's nuclear programme, Pence said, adding that the era of US "strategic patience" in dealing with the regime was over.

Washington is worried that North Korea may soon build a nuclear-tipped missile that could reach the United States.

Like South Korea, Japan already faces a direct threat from the secretive regime.

In February, the North simultaneously fired four ballistic missiles off its east coast, three of which fell provocatively close to Japan, in what it said was a drill for an attack on US bases in the country.

Pence's Japanese hosts will likely be cautious about any US military action that could trigger a broader regional conflict.

Their hope is that the White House will focus on pressuring China, Pyongyang's only major ally and biggest trade partner, to redouble its efforts to rein in the regime and prompt North Korea to return to the negotiating table after it abandoned the six-party talks in 2009.

"With close coordination, I expect we will strongly demand North Korea to refrain from taking provocative actions and to adhere to UN Security Council resolutions," said Japanese government spokesman Yoshihide Suga.

Pence's trip will also feature a heavy economic focus.

Trump's decision to scrap a 12-nation trans-Pacific trade deal was a blow to Prime Minister Shinzo Abe, who expended substantial political capital to get the deal passed at home.

In Tokyo, there is still hope that the core of the agreement, thrashed out between the United States and Japan and intended to counterbalance China's regional economic power, can be salvaged in some form.

But US officials say expectations of an ambitious bilateral trade deal may be premature.